[Ultrastructural and histochemical criteria of myocardial hypoxia and a morphological assessment of the various methods for its protection (based on biopsy data of the human heart)].

Short-term ischemia (up to 10 minutes) induced by clamping of the aorta in correction of a ventricular septal defect causes no essential ultrastructural, metabolic or functional changes in the myocardium. In much longer period of ischemia (of up to 40 minutes) during operation for congenital heart diseases, the use of deep hypothermia is effective. Cold cardioplegia is a sufficiently reliable method for myocardial protection when the aorta is clamped for up to 60 minutes in operations for acquired heart diseases. Changes in the structure and metabolism of the myocardium are reparable, their degree depends on the initial condition of the heart muscle and proper fulfilment of the methodical conditions of this type of protection. Pharmacological cardioplegia combined with external cooling of the heart makes it safe to disconnect the heart from circulation for a loger period (up to 120 minutes).